Half-Squares on 30–10 m: Feed Them at the Corner (or Center), Not the End

Why a 49:1 “seems to work” but really doesn’t — and what ratio actually fits a half-square

What a Half-Square Is — and Why We Like It

A half-square is simply a half-wavelength horizontal wire with a quarter-wavelength vertical wire hanging from each end. The two verticals act like a pair of in-phase, ¼λ vertical radiators; the top wire is the phasing section. Properly built, the pattern is bi-directional broadside to the array with a low take-off angle — great for DX.

Classic modeling by L. B. Cebik (W4RNL) shows that a corner feed can be arranged for a near-50 Ω match and deliver low-angle radiation at modest heights.

Corner feed (current-fed): 50–70 Ω is achievable on the design band; no matching transformer is needed — just a 1:1 current choke at the feedpoint.
End feed (voltage-fed): presents several kΩ ± jX and is not suitable for direct coax feed.

In short: if you want “~50 Ω ±,” feed at a corner (or at the midpoint of the top wire with a 1:1 choke) — not at the end.

“But My 49:1 Shows a Nice SWR…” — Why That’s Misleading

A 49:1 transformer works well for true end-fed half-waves (2–5 kΩ), but not for half-squares:

• The half-square’s end isn’t 2.5 kΩ. The impedance is usually much higher and reactive, shifting wildly with height and surroundings.
• The SWR still looks “okay” due to the shunt capacitor. Many EFHW boxes include a 68–150 pF capacitor on the low-Z side, pulling the impedance locus and “flattening” the analyzer trace. It looks good but isn’t efficient.
• Common-mode “cheats.” The feedline often becomes the missing return path, masking mismatch and radiating from the coax. The transformer runs hot while efficiency drops.

Bottom line: a 49:1 on a half-square can show a pretty SWR curve but is not performing a true 49:1 transformation to the antenna’s R + jX.

Why ~17–23:1 Is Closer to Reality

When reusing a 30 m half-square on higher bands, corner or mid-top impedances often fall between 600 Ω and 1400 Ω. That equates to ~12–28:1 impedance ratio — typically ~17–23:1 (≈ 850–1150 Ω) in real environments.

That means a turns ratio near √20 ≈ 4.5 : 1 (e.g., 2 : 9 or 3 : 13 windings), not the 7 : 1 used for 49 : 1. Still, such a transformer won’t fix large reactances — it’s only part of the story.

Voltage-Fed vs Current-Fed — and Why Height Matters

Voltage-fed (end-fed) points excite a voltage maximum / current minimum. They’re:

• highly sensitive to stray capacitance (supports, foliage, rain),
• prone to feedline common-mode currents, and
• lossy when mismatched or poorly choked.

Current-fed (corner or mid-top) drives a current maximum in the air, improving pattern stability and efficiency. A simple 1:1 current choke suffices for clean operation.

Height matters: a top-wire height of ~0.20–0.25 λ gives low-angle DX radiation. Too high grows a high-angle lobe and spoils the advantage.

(End-fed setups require even more clearance at the high-voltage point, often defeating the half-square’s simplicity on 30–20 m.)

Recommended Ways to Feed a 30–10 m Half-Square

Corner-feed (best single-band, ~50 Ω)

• Connect the coax center to the top wire’s end and shield to the top of the adjacent vertical.
• Add a 1:1 current choke right at the feed (≥5–10 kΩ CM impedance on your band).
• Trim for resonance; expect near-50 Ω direct feed.

Mid-top feed (balanced, low-Z)

• Feed the center of the top half-wave through a 1:1 balun or balanced line.
• Gives another near-50 Ω option at a current maximum.

Avoid: End-feeding with a 49 : 1 — it’s meant for a true EFHW (~2–5 kΩ), not a half-square. The capacitor and strays only simulate a good SWR while efficiency collapses.

Quick-Start Lengths

Use these starting cuts (approximate free-space shortening included). Top = ½λ; each vertical = ¼λ.

(Expect trimming for height, wire diameter, and environment; geometry shifts resonance and impedance.)

Take-Aways

• Feed at the corner (or mid-top) for ~50 Ω and stable currents.
• A 49 : 1 is for EFHWs (~2–5 kΩ) — not for half-squares; the capacitor just hides the mismatch.
• Typical feed impedances ~600–1400 Ω imply ~17–23 : 1 transform ratio if needed, not 49 : 1.
• Keep top-wire height around 0.2–0.25 λ for low angles; end-fed variants need more clearance and often lose their purpose.

References & Notes

• L. B. Cebik (W4RNL): SCVs Part 4 — The Open-Ended Cousins (half-square modeling and feed studies)
• W8JI: End-fed and J-pole analysis — voltage vs current feed behavior
• OnAllBands (DX Engineering): typical EFHW end impedances (~1–5 kΩ) and matching notes
• WVARA / KN5L / AI6XG presentations: the shunt-capacitor effect in EFHW boxes (flat SWR ≠ efficiency)

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